Cabazitaxel is a semi-synthetic derivative of the natural taxoid 10-deacetylbaccatin III, commercialized as acetone solvate. It stabilizes microtubules leading eventually to the mitotic arrest of proliferating cells. It has been approved in the United States of America for the second line treatment of hormone-refractory prostate cancer following a docetaxel-based treatment.
Cabazitaxel has the following formula (I):

Its chemical name is 4α-acetoxy-2α-benzoyloxy-5β-epoxy-1β-hydroxy-7β, 10β-dimethoxy-9-oxo-11-taxen-13α-yl (2R,3S)-3-tert-butoxycarbonylamino-2-hydroxy-3-phenylpropionate.
Cabazitaxel and methods for the preparation thereof are described in WO96/30355 and in WO99/25704.
WO2005/028462 describes an acetone solvate of Cabazitaxel, sometimes referred to as form A. Despite the fact that crystallisation of the acetone solvate is a very effective way for removing impurities, a better pharmaceutical form will be pure Cabazitaxel without any crystallization solvent.
Additional crystalline solvate forms of Cabazitaxel referred to as form I (toluene solvate), form II (methyl tert-butyl ether solvate), form III (2-propanol solvate), form IV (1-butanol solvate), form V (1-propanol solvate) and an amorphous form of Cabazitaxel in a powdery, non-foamy form are described in WO2012/142117 (Teva). Solvates are rarely used in pharmaceuticals because the solvents are volatile thus making it difficult to maintain the solvent in the crystal. If the API desolvates due to storage conditions or otherwise, it could lead to the formation of multiple polymorphs with different physical properties. Additionally, amorphous solids are metastable and can lead with time to the formation of different polymorphs with different physical properties.
WO2009/115655 (Sanofi) discloses five anhydrous forms of the compound, referred to as forms B, C, D, E and F; three ethanol solvates, referred to as ethanolate forms B, D, E; an ethanol/water heterosolvate form F; and a monohydrate-solvent free form C and a dihydrate-solvent free form C. Reaching high purities with these forms is only possible providing the API has been previously purified by other techniques such as for example passing through the acetone solvate (as described in the application). However the introduction of a further purification technique hampers the manufacturing process with inefficiency due to longer production times and lower yield.
WO 2013/134534 discloses crystalline Cabazitaxel solvates with:                alkyl acetates, such us the solvates with ethyl acetate (Form VII), isopropyl acetate (Form VIII), methyl acetate (Form XVII), butyl acetate (Form XVIII) and isobutyl acetate (Form XXI);        ketones, such as the solvates with methyl ethyl ketone (Form IX) and methyl isobutyl ketone (Form X);        alcohols, such as the solvates with 2-butanol (Form XI), isobutanol (Form XII) and amyl alcohol (Form XIII).        
WO 2013/134534 also describes solvates with dioxolane (Form XIV), 1,4-dioxane (Form XV), 1,2-propanediol (Form XIX), glycerol (Form XX) and 1,3-dimethy-2-imidazolidinone (Form XXII). A crystalline Cabazitaxel form designated as Form XVI, which may be anhydrous, is also disclosed.
A crystalline ethyl acetate solvate of Cabazitaxel is disclosed also in WO 2013/088335.
WO2009/115655 discloses two hydrate forms of the compound in particular mono and di-hydrate, both hydrate forms are obtained from anhydrous form C by exposition to moisture. The anhydrous form C as described above is obtained in high purity only by passing through the acetone solvate.
A crystalline form of Cabazitaxel obtained from acetone/water is described in CN 102675257 A.
Crystalline forms, including an anhydrate form, of Cabazitaxel, designated as Forms C1, C2, C3, C4, C5, C6, C7, C8, C8b, C9 and C9p are described in WO2013/034979.
Finally, 13 crystalline forms referred to as Form-1, Form-2, Form-3, Form-4, Form-5, Form-6, Form-7, Form-8, Form-9, Form-10, Form-11, Form-12, and Form-13 are disclosed in WO2013/0109870.
It is still desirable to find new crystalline forms able to solve the aforementioned problems.